Add v1.x deprecation warning

icepyx/__init__.py

@@ -1,3 +1,15 @@
+from warnings import warn
+
+deprecation_msg = """icepyx v1.x is deprecated; the back-end systems on which is relies
+are being shut down. Please upgrade to icepyx v2.x which uses the new NASA Harmony
+back-end.
+"""
+# IMPORTANT: This is being done before the other icepyx imports because the imported
+# code changes warning filters. If this is done after the imports, the warning won't
+# work.
+warn(deprecation_msg, DeprecationWarning, stacklevel=2)
+
+
 from _icepyx_version import version as __version__
 
 from icepyx.core.query import GenQuery, Query